Project Summary Sleep apnea is a major risk for Alzheimer's disease (AD) and related dementias (ADRD); however, such findings are limited to non-Hispanic whites. There are currently scientific gaps in knowledge about AD risk among Latinos, the largest US ethnic minority. Latinos have a 4-fold increased risk of AD and a 2-fold risk of stroke and cardiovascular diseases, compared to non-Hispanic whites. Of importance, the prevalence of AD and sleep apnea varies across the Latino groups, with higher prevalence among Latinos of Caribbean background. Yet, the current scientific base lacks evidence on the connections and mechanisms between sleep apnea, vascular disease and ADRD, especially among middle-aged and older Latinos. In this study, we efficiently leveraged the baseline and second-wave data of the Hispanic Community Health Study/Study of Latinos (SOL; N=16,415). SOL provides extensive and detailed data on sociocultural, genetic, and cardiovascular risk factors. At baseline, SOL obtained home-sleep test in over 16,000 participants and sleep habits through questionnaires and actigraphy, in a subsample of 2,252 SOL participants. SOL is complemented by the SOL-Investigation of Neurocognitive Aging (SOL-INCA; AG48642) study, which evaluates the prevalence of neurocognitive decline, Mild Cognitive Impairment (MCI) and ADRD among middle-aged and older Latinos of diverse national backgrounds. We hypothesized that sleep apnea, which starts in middle age, disrupts proper neurovascular function and contribute to early neurocognitive decline and MCI/ADRD. We propose to do an exploratory analyses of baseline sleep data and prospective neurocognitive tests, to evaluate 1) the effect of baseline sleep apnea on neurocognitive decline and MCI/ADRD, 2) determine if sleep apnea partly mediates associations between cardiovascular risk factors, neurocognitive decline and MCI/ADRD, and 3) explore actigraphy defined sleep duration and sleep fragmentation as predictors of MCI/ADRD in SOL participants. In synergy with SOL- INCA, our study works within a novel neurovascular developmental approach to understand early neurocognitive decline. We also use culturally sensitive methods among people of diverse Latino backgrounds. This study provides the framework for future SOL studies on sleep and ADRD in Latinos. Evaluating the severity of baseline sleep apnea, levels of hypoxemia, apnea duration, sleep duration and sleep fragmentation, provides an opportunity to refine the sleep phenotypes associated to early neurocognitive decline and MCI/ADRD. This will provide the preliminary data necessary to inform the sleep variables needed for comprehensive sleep assessments with polysomnography and quantitative electroencephalogram. In addition to allowing longitudinal evaluations of sleep and neurocognitive tests to be obtained at SOL visit three.